AP* Chemistry ATOMS, MOLECULES & IONS

AP* Chemistry ATOMS, MOLECULES & IONS

2.1 THE EARLY HISTORY OF CHEMISTRY • • • • The highest honor given by the American Chemical Society. He discovered oxygen. Ben Franklin got him interested in electricity and he observed graphite conducts an electric current. Politics forced him out of England and he died in the US in 1804. The back side, pictured below was given to Linus Pauling in 1984. Pauling was the only person to win Nobel Prizes in TWO Different fields: Chemistry and Peace.

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1,000 B.C.—processing of ores to produce metals for weapons and ornaments; use of embalming fluids 400 B.C.—Greeks—proposed all matter was make up of 4 “elements” : fire, earth, water and air Democritus—first to use the term atomos to describe the ultimate, smallest particles of matter Next 2,000 years—alchemy—a pseudoscience where people thought they could turn metals into gold. Some good chemistry came from their efforts—lots of mistakes were made! 16th century—Georg Bauer, German , refined the process of extracting metals from ores & Paracelsus, Swiss, used minerals for medicinal applications Robert Boyle, English—first “chemist” to perform quantitative experiments of pressure versus volume. Developed a working definition for “elements”. 17th & 18th Centuries—Georg Stahl, German—suggested “phlogiston” flowed OUT of burning material. An object stopped burning in a closed container since the air was “saturated with phlogiston” Joseph Priestley, English—discovered oxygen which was originally called “dephlogisticated air”

2.2 FUNDAMENTAL CHEMICAL LAWS

late 18th Century—Combustion studied extensively CO2, N2, H2 and O2 discovered list of elements continued to grow Antione Lavoisier, French—explained the true nature of combustion—published the first modern chemistry textbook AND stated the Law of Conservation of Mass. The French Revolution broke out the same year his text was published. He once collected taxes for the government and was executed with a guillotine as an enemy of the people in 1794. He was the first to insist on quantitative experimentation. • • • •

THE LAW OF CONSERVATION OF MASS: Mass is neither created nor destroyed.Joseph Proust, French—stated the Law of Definite Proportions

*AP is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product. © 2008 by René McCormick. All rights reserved.

THE LAW OF DEFINITE PROPORTIONS: A given compound always contains exactly the same proportions of elements by mass. •

1808--John Dalton stated the Law of Definite proportions. He then went on to develop the Atomic Theory of Matter.

THE LAW OF MULTIPLE PROPORTIONS: When two elements combine to form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. Dalton considered compounds of carbon and oxygen and found: Mass of Oxygen that combines with 1 gram of C Compound I 1.33 g Compound II 2.66 g Therefore Compound I may be CO while Compound II may be CO2. Exercise 2.1 Illustrating the Law of Multiple Proportions The following data were collected for several compounds of nitrogen and oxygen:

Mass of Nitrogen That Combines With 1 g of Oxygen Compound A Compound B Compound C

1.750 g 0.8750 g 0.4375 g

Show how these data illustrate the law of multiple proportions. A = 1.750 = 2 B 0.875 1 B = 0.875 = 2 C 0.4375 1 A = 1.750 = 4 C 0.4375 1

Atoms, Molecules and Ions

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2.3 DALTON’S ATOMIC THEORY Dalton’s ATOMIC THEORY OF MATTER: (based on knowledge at that time): 1. All matter is made of atoms. These indivisible and indestructible objects are the ultimate chemical particles. 2. All the atoms of a given element are identical, in both weight and chemical properties. However, atoms of different elements have different weights and different chemical properties. 3. Compounds are formed by the combination of different atoms in the ratio of small whole numbers. 4. A chemical reaction involves only the combination, separation, or rearrangement of atoms; atoms are neither created nor destroyed in the course of ordinary chemical reactions. **TWO MODIFICATIONS HAVE BEEN MADE TO DALTON' S THEORY 1. Subatomic particles were discovered. 2. Isotopes were discovered. •

1809 Joseph Gay-Lussac, French—performed experiments [at constant temperature and pressure] and measured volumes of gases that reacted with each other.

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1811 Avogardro, Italian—proposed his hypothesis regarding Gay-Lussac’s work [and you thought he was just famous for 6.02 x 1023] He was basically ignored, so 50 years of confusion followed.

AVOGADRO’S HYPOTHESIS: At the same temperature and pressure, equal volumes of different gases contain the same number of particles.


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2.4 EARLY EXPERIMENTS TO CHARATERIZE THE ATOM Based on the work of Dalton, Gay-Lussac, Avogadro, & others, chemistry was beginning to make sense [even if YOU disagree!] and the concept of the atom was clearly a good idea! THE ELECTRON •

J.J. Thomson, English (1898-1903)—found that when high voltage was applied to an evacuated tube, a “ray” he called a cathode ray [since it emanated from the (-) electrode or cathode when YOU apply a voltage across it] was produced. o The ray was produced at the (-) electrode o Repelled by the (-) pole of an applied electric field, E o He postulated the ray was a stream of NEGATIVE particles now called electrons, e-

o

He then measured the deflection of beams of e- to determine the charge-to-mass ratio

e C = − 1 .7 6 × 1 0 8 m g o e is charge on electron in Coulombs, (C) and m is its mass. o Thomson discovered that he could repeat this deflection and calculation using electrodes of different metals ∴ all metals contained electrons and ALL ATOMS contained electrons o Furthermore, all atoms were neutral ∴ there must be some (+) charge within the atom and the “plum pudding” model was born. Lord Kelvin may have played a role in the development of this model. [the British call every dessert pudding—we’d call it raisin bread where the raisins were the electrons randomly distributed throughout the + bread] •


1909 Robert Millikan, American—University of Chicago, sprayed charged oil drops into a chamber. Next, he halted their fall due to gravity by adjusting the voltage across 2 charged plates. Now the voltage needed to halt the fall and the mass of the oil drop can be used to calculate the charge on the oil drop which is a whole number multiple of the electron charge. Mass of e- = 9.11 × 10-31 kg.

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RADIOACTIVITY •

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Henri Becquerel, French—found out quite by accident [serendipity] that a piece of mineral containing uranium could produce its image on a photographic plate in the absence of light. He called this radioactivity and attributed it to a spontaneous emission of radiation by the uranium in the mineral sample. THREE types of radioactive emission: o alpha, α--equivalent to a helium nucleus; the largest particle radioactive particle emitted; 7300 times the mass of an electron. 24 He Since these are larger that the rest, early atomic studies often involved them. o beta, β--a high speed electron. −10 β OR −10 e o gamma, γ--pure energy, no particles at all! Most penetrating, therefore, most dangerous.

THE NUCLEAR ATOM •

1911 Ernest Rutherford, England—A pioneer in radioactive studies, he carried out experiments to test Thomson’s plum pudding model. o Directed α particles at a thin sheet of gold foil. He thought that if Thomson was correct, then the massive α particles would blast through the thin foil like “cannonballs through gauze”. [He actually had a pair of graduate students Geiger & Marsden do the first rounds of experiments.] He expected the α particles to pass through with minor and occasional deflections.

o

The results were astounding [poor Geiger and Marsden first suffered Rutherford’s wrath and were told to try again—this couldn’t be!]. Most of the α particles did pass straight through, BUT many were deflected at LARGE angles and some even REFLECTED! Rutherford stated that was like “shooting a howitzer at a piece of tissue paper and having the shell reflected back”. He knew the plumb pudding model could not be correct! Those particles with large deflection angles had a “close encounter” with the dense positive center of the atom Those that were reflected had a “direct hit” He conceived the nuclear atom; that with a dense (+) core or nucleus


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This center contains most of the mass of the atom while the remainder of the atom is empty space!

2.5 THE MODERN VIEW OF ATOMIC STRUCTURE: AN INTRODUCTION ELEMENTS All matter composed of only one type of atom is an element. There are 92 naturally occurring, all others are manmade. ATOMS atom--the smallest particle of an element that retains the chemical properties of that element. • nucleus--contains the protons and the neutrons; the electrons are located outside the nucleus. Diameter = 10-13 cm. The electrons are located 10-8cm from the nucleus. A mass of nuclear material the size of a pea would weigh 250 million tons! Very dense! proton--positive charge, responsible for the identity of the element, defines atomic number neutron--no charge, same size & mass as a proton, responsible for isotopes, alters atomic mass number electron--negative charge, same size as a proton or neutron, BUT 1/2,000 the mass of a proton or neutron, responsible for bonding, hence reactions and ionizations, easily added or removed. • atomic number(Z)--The number of p+ in an atom. All atoms of Particle Mass Charge the same element have the same number of p+. -31 e 9.11 × 10 1• mass number(A)--The sum of the number of neutrons and p+ + -27 for an atom. A different mass number does not mean a different p 1.67 × 10 1+ element--just an isotope. n0 1.67 × 10-27 None mass number → atomic numbe r→

A Z

Χ

← element symbol

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actual mass is not an integral number! mass defect--causes this and is related to the energy binding the particles of the nucleus together Exercise 2.2 Writing the Symbols for Atoms Write the symbol for the atom that has an atomic number of 9 and a mass number of 19. How many electrons and how many neutrons does this atom have?

F; 9 electrons and 10 neutrons


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ISOTOPES • isotopes--atoms having the same atomic number (# of p+) but a different number of neutrons • most elements have at least two stable isotopes, there are very few with only one stable isotope (Al, F, P) • hydrogens isotopes are so important they have special names: 0 neutrons ) hydrogen 1 neutron ) deuterium 2 neutrons ) tritium 2.6 MOLECULES AND IONS Electrons are responsible for bonding and chemical reactivity • • • • •

Chemical bonds—forces that hold atoms together Covalenet bonds—atoms share electrons and make molecules [independent units]; H2, CO2, H2O, NH3, O2, CH4 to name a few. molecule--smallest unit of a compound that retains the chem. characteristics of the compound; characteristics of the constituent elements are lost. molecular formula--uses symbols and subscripts to represent the composition of the molecule. (Strictest sense--covalently bonded) structural formula—bonds are shown by lines [representing shared e- pairs]; may NOT indicate shape

H

O

H

O H

•

H

ions--formed when electrons are lost or gained in ordinary chem. reactions; affect size of atom dramatically • cations--(+) ions; often metals since metals lose electrons to become + charged • anions--(-) ions; often nonmetals since nonmetals gain electrons to become - charged • polyatomic ions--units of atoms behaving as one entity ) MEMORIZE formula and charge! • ionic solids—Electrostatic forces hold ions together. Strong ∴ ions held close together ∴ solids.


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2.7 AN INTRODUCTION TO THE PERIODIC TABLE

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Atomic number = number of protons and is written above each symbol metals—malleable, ductile & have luster; most of the elements are metals—exist as cations in a “sea of electrons” which accounts for their excellent conductive properties; form oxides [tarnish] readily and form POSITIVE ions [cations]. Why must some have such goofy symbols?

Current Name Antimony Copper Iron Lead Mercury Potassium Silver Sodium Tin Tungsten

Original Name Stibium Cuprum Ferrum Plumbum Hydrargyrum Kalium Argentum Natrium Stannum Wolfram

Symbol Sb Cu Fe Pb Hg K Ag Na Sn W

groups or families--vertical columns; have similar physical and chemical properties (based on similar electron configurations!!) • group A—Representative elements • group B--transition elements; all metals; have numerous oxidation/valence states periods--horizonal rows; progress from metals to metalloids [either side of the black “stair step” line that separates metals from nonmetals] to nonmetals MEMORIZE: 1. ALKALI METALS—1A 2. ALKALINE EARTH METALS—2A 3. HALOGENS—7A 4. NOBLE (RARE) GASSES—8A


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2.8 NAMING SIMPLE COMPOUNDS BINARY IONIC COMPOUNDS Naming + ions: usually metals • monatomic, metal, cation → simply the name of the metal from which it is derived. Al3+ is the aluminum ion • transition metals form more than one ion; Roman Numerals (in) follow the ion=s name. Cu2+ is copper(II) (Yeah, the no space thing between the ion’s name and (II) looks strange, but it is the correct way to do it.) Mercury (I) is an exception ) it is Hg22+ ∴ two Hg+ associated together. NH4+ is ammonium NO ROMAN NUMERAL WHEN USING silver, cadmium and zinc. [Arrange their SYMBOLS in alphabetical order—first one is 1+ and the other two are 2+] Naming - ions: monatomic and polyatomic • MONATOMIC--add the suffix -ide to the stem of the nonmetal's name. Halogens are called the halides. • POLYATOMIC--quite common; oxyanions are the PA's containing oxygen. hypo--”ate” least oxygen -ite--”ate” more oxygen than hypo-ate--”ate” more oxygen than -ite hyper---ate--”ate” the most oxygen NAMING IONIC COMPOUNDS: The + ion name is given first followed by the name of the negative ion. • •


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Exercise 2.3 Naming Type I Binary Compounds Name each binary compound. a. CsF b. A1C13 c. LiH

a. cesium fluoride b. aluminum chloride c. lithium hydride

Exercise 2.4 Naming Type II Binary Compounds Give the systematic name of each of the following compounds. a. CuC1 b. HgO c. Fe2O3 d. MnO2 e. PbC12 a. copper(I) chloride, b. mercury(II) oxide. c. iron(III) oxide. d. manganese(IV) oxide. e. lead(II) chloride.

TYPE II: Involve a transition metal that needs a roman numeral Mercury (I) is Hg2

+2

Exceptions: these never need a roman numeral even though transition metals. MEMORIZE Ag+, Cd2+, Zn2+


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Exercise 2.5 Naming Binary Compounds Give the systematic name of each of the following compounds. a. CoBr2

b. CaC12

c. A12O3

d. CrC13

a. b. c. d.

Cobalt(II) bromide Calcium chloride Aluminume oxide Chromium(III) chloride

Exercise 2.6 Naming Compounds Containing Polyatomic Ions Give the systematic name of each of the following compounds. a. Na2SO4 e. Na2SO3 i. NaOC1

b. KH2PO4 f. Na2CO3 j. Na2SeO4

c. Fe(NO3)3 g. NaHCO3 k. KBrO3

d. Mn(OH)2 h. CsC1O4

a. Sodium sulfate b. Potassium dihydrogen phosphate c. Iron(III) nitrate d. Manganese(II) hydroxide e. Sodium sulfite f. Sodium carbonate g. Sodium hydrogen carbonate h. Cesium perchlorate i. Sodium hypochlorite j. Sodium selenate k. Potassium bromate

NAMING BINARY COVALENT COMPOUNDS : (covalently bonded) • use prefixes!!! Don’t forget the –ide ending as well. Exercise 2.7

Naming Type III Binary Compounds

Name each of the following compounds. a. PC15

b. PC13

c. SF6

d. SO3

e. SO2

f. CO2

a. Phosphorus pentachloride b. Phosphorus trichloride c. Sulfur hexafluoride d. Sulfur trioxide e. Sulfur dioxide f. Carbon dioxide Atoms, Molecules and Ions

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ACIDS •

hydrogen, if present, is listed first naming acids ) -ide → hydro [negative ion root]ic ACID -ate → -ic ACID -ite → -ous ACID


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Exercise 2.8

PAINS IN THE GLUTEUS MAXIMUS: these lovely creatures have been around longer than the naming system and no one wanted to adapt!! water ammonia hydrazine phosphine nitric oxide nitrous oxide (“laughing gas”)

Naming Various Types of Compounds

Give the systematic name for each of the following compounds. a. P4O10

b. Nb2O5

c. Li2O2

d. Ti(NO3)4 a. Tetraphosphorus decaoxide b. Niobium(V) oxide c. Lithium peroxide d. Titanium(IV) nitrate

Exercise 2.9 Writing Compound Formulas from Names Given the following systematic names, write the formula for each compound. a. Vanadium(V) fluoride c. Rubidium peroxide

b. Dioxygen difluoride d. Gallium oxide a. VF5 b. O2F2 c. Rb2O2 d. Ga2O3


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